Although the CLAIRO project deals specifically with the use of urban greenery to reduce concentration of air pollutants, the conference took a broader look at the beneficial role of greenery in an urban setting. Apart from air quality, the speakers touched upon different aspects of healthy urban living, from human-centric mobility, climate resilience and heat stress mitigation, integration of blue, green and grey spaces, and planning green spaces for positive health outcomes. The event was closed in the afternoon by workshop sessions presenting the main conclusions of the ongoing research within the CLAIRO project.
The aim of the conference was to give a final boost to dissemination efforts under CLAIRO, shedding light on key findings of the project and conveying an essential message about the relevance of urban greening. The first speaker of the event, Gabriela Kaluzova from SOBIC, a research and innovation involved in the CLAIRO project consortium, provided an overview of the key activities of the project. Kaluzova highlighted that
The UIA programme has significantly influenced the choice of the solution how to face air pollution in Ostrava.
She has stressed that as the UIA programme supports only highly innovative approaches in European level, the CLAIRO partnership strived to look for a solution that is unprecedented in Europe, to test it and implement it in Ostrava and to share the gained knowledge with the rest of Europe. The involvement of three universities in the CLAIRO partnership were crucial in ensuring that a really innovative approach was developed. All the key steps taken in the project were explained in detail in a Methodology document targeting at experts.
In the afternoon workshop session, the main role was played by partners of the CLAIRO consortium. In his talk, Vit Kaspar from the Silesian University in Opava provided guidance on how to plant urban vegetation for maximum pollutant capture and how to model air pollution removal by greenery. He has stated that a rapid increase in modelled air pollution removal was confirmed in the project after greenery planting. Kaspar has summarized one of the key findings of CLAIRO:
Especially trees and mostly large trees have a role in improving urban air quality through dry deposition among other mechanisms. Therefore, it is needed to sustain large trees in public spaces apart from investing in planting new greenery.
Pavel Bucek from the Technical University of Ostrava explained how air quality data was used for greenery planting in Ostrava and shared thoughts about the benefits of the sensor technology used in monitoring. Karel Dolezal from the Palacky University Olomouc outlined how the resilience of greenery can be strengthened by biofertilizers. Finally, Gabriela Kaluzova gave an account of the results of a public survey conducted under CLAIRO on the perception of air quality and urban greenery.
Moving from car-centric urban development to people-friendly cities
Peter Bednar, an architect and urban planner working at Jakub Cigler Architekti (JCA) in Prague in his presentation during the morning session focused on the impacts of transport on urban planning, land use and quality of life, and the necessity of a transition from a car-centred planning to a more balanced, human-centric urban development.
He has highlighted that urban transport is incredibly important in cities, as cities are largely composed through traffic. In modern cities urban development is completely based on speed and the geometry of automobiles leading to an unfortunate distribution of land.
According to Bednar, car-oriented development creates a vicious circle that he has termed as ‘urban doom’, in which several elements intensify and aggravate each other leading to a worsening of the situation. First cities build infrastructure to accommodate increasing amounts of cars, which will reduce available funding for other transport modes. As a consequence, underfunded public transport and poor walkability of neighbourhoods will lead to the stigmatization of walking and the use of public transport, promoting car-centric planning and pushing people into cars. These developments result in excessive and undesirable urbanization on the fringes of the city, forcing residents to use cars for every trip they make. As a result, all new developments will have very low density and connectivity integrating vast new areas offering parking places to accommodate the needs of the increasing number of car users and to reduce the pressure on city centres that struggle with a lack of parking space. Finally, due to this robust suburbanization, car is required for most of the trips triggering the development of new infrastructure for passenger cars and with this the vicious circle has been closed.
Bednar has highlighted that
The irony is that people who want to escape the city and traffic and noise and everything else, are the ones who create this traffic problem by living in an area that cannot be serviced by any other means of transport, except private car.
There are large number of green areas in the suburban zone, but these green areas can mainly be accessed by car. Accordingly, more green spaces actually means that residents of the urban fringe will rely only on car and will drive almost everywhere.
Car-oriented development has substantial drawbacks. First, it is expensive, as according to Bednar, suburban development can be seven times more expensive than compact city centre development. Then, it wastes land, it creates distances that can be covered only by car, contributes to environmental, social and economic degradation and also triggers the construction of unattractive buildings.
As a counterpoint to car-centric urban development, the City of Paris has recently embraced the ’15- Minute City’ concept. In a 15- Minute City daily necessities are located within a short walk or bike ride from the homes of residents.
Peter Bednar has warned though that one has to be careful with the concept, as very rarely can all working places, stores, services and housing be placed in a way that everything is accessible within 15 minutes. In his view, the problem with the 15-minutes city is that, as the concept is centred on short distances, it might not have enough inhabitants to support services. According to Bednar’s estimation, a 15-minute city can accommodate 5,000 people at most. This population can hold a petrol station and a pub, but will not necessarily sustain specialty stores, bookstores or florists and other services that are associated with the urban qualities of the 15-minute city. To be really effective, a 15-minutes city has to have exceptionally high density, with a population of at least 15,000 people.
A way out could be to develop a 30-minute city of comfortable distances instead of a 15-minute city of short distances. This can be done by densifying suburban areas and by focusing on short travel time instead of short distances. The result is a polycentric city with high density that offers many options for transport. Car is one of them but necessarily not the only one.
The carrying capacity of a street can differ significantly by transport mode. One km of roadway accommodates only about 30 cars with 50 people, while one km of road offering public transit accommodates hundreds of people, and one km of sidewalk can accommodate even thousands of people. Therefore, if in a typical street in an urban centre a car lane is replaced or narrowed by different services, such as greenery, a bus lane or wider sidewalks, similar or increased traffic capacity can be achieved that will be accompanied with many other benefits.
Summarizing the main learning points, Peter Bednar highlighted that
Cities are places where traffic should slow down and stop. We need places to stay and minimize places for passing through. We need to consume less land, build more buildings on it, create more destinations attracting more people, giving them more options that will result in better traffic.
Green spaces deliver positive physical and mental health outcomes
The role of green spaces in delivering positive physical and mental health outcomes and their contribution to healthy city planning were addressed by Eduarda Marques da Costa, an associate professor of Institute of Geography & Spatial Planning in her presentation.
In her presentation da Costa went through the most important factors that can influence the level of impact of green spaces on health.
The scale of the intervention, that can range from individual scale to city scale significantly affect its impact and limits design options. Proximity is also relevant as green spaces seem to be more relevant to potential users if the distance to them is under 400 meters. Population characteristics, such as age, gender, level of disability, level of education and other socio-economic conditions like employment and income are also important influencing factors. Active population and children are typically more frequent users of green spaces than older people.
Eduarda Marques da Costa has underlined that
The provision of green spaces in urban settings is a valuable measure for promoting health, wellbeing and quality of life and for supporting the creation of places for relaxation, recreation and social interaction.
Modification of the design of hard surfaces can help create liveable streetscapes
In his presentation Martin Vysoky, a landscape architect at Edge, outlined how can blue, green and grey systems (in other words water, vegetation and hard surfaces) be integrated to form a multifunctional streetscape with an aim to create liveable and resilient urban neighbourhoods.
In Stockholm a very successful street tree planting program has been developed since 2001, which resulted in tree growth in downtown sidewalks that is equal to or even better than trees growing in nearby parks.
In urban environment, as Vysoky has highlighted trees often struggle with insufficient root space and soil compaction,leading to poor water, oxygen and nutrient uptake. Under wet conditions in soils with high clay content, which are typical in Stockholm, the clay aggregated can easily collapse, resulting in very dense and compact soils. It was observed by urban practitioners in Sweden, that if macadam or sand-based soils are used in an urban area instead of clay-based soils, then this problem does not arise, since in such soils there is nothing that could collapse.
When the City of Stockholm embarked on a quest to develop climate resilient system solutions for urban areas, the focus shifted to hard surfaces that are the most dominant elements of the streetscape. The subbase, the lowest layer of the pavement, supports most of the volume of the hard surface. The subbase that is typically composed of crushed stone does not provide space for root growth and water. To hinder soil compaction, crushed stone with its fine particles in the subbase is replaced with coarser macadam, traditionally used in the construction of railways. The result is an Open Subbase Layer (OSL) with high porosity providing sufficient space for water, roots and oxygen and at the same time bearing the traffic load.
According to Vysoky the Open Subbase Layer provides a robust basis for the development of complex blue-green-grey systems. It offers flexibility for working with different sections during the planning of streetscapes. It allows the development of raingardens, vegetation beds or tree pits and constructions can be built on top of it. The system with its high porosity provides a possibility to take care of stormwater runoffs from rooftops and nearby hard surfaces. The voids between the rocks are filled with humus-based planting substrate when tree pits or vegetation beds are created.
Martin Vysoky emphasized that
We can see that if we create space for the roots, they will go deep and create this fantastic dense structure under the hard surfaces without damaging them.
With the help of this multifunctional system, hard surfaces can be effectively integrated with a vegetation function. Lately in the last 10 years a water retention function was also added to the system developed in Sweden and as a result trees perform really well even during heatwaves.
Greenery helps cities adapt to heat
Birgit Georgi, a climate adaptation expert, focused on the potential of nature-based solutions to reduce climate change impacts in cities. She has emphasized that
We need to tackle climate change not only with mitigation but also by adaptation measures.
She was highlighting that vegetation can be beneficial in tackling heat by reducing the heat storage capacity of urban surfaces, by reducing air temperature by shading and increased evapotranspiration, by supporting ventilation and bringing cool air into the city.
Georgi brought an exciting example showing the effectiveness of greenery in cooling cities. The results of an urban climate model developed by the city of Salzburg suggests that massive greening measures that are smartly planned can have the potential to effectively mitigate overheating of cities in the future. According to the findings of the modelling made for Salzburg, if the reflectivity of sealed surfaces would be doubled, and at the same time sealed surfaces would be reduced by 30%, every second rooftops would be greened, the number of trees would be increased by 50%, and bare soil would be replaced with grass, then in 2050 there would be the same number of hot days as in 1981-2010.
As it was stressed by Georgi, if all additional benefits of vegetation are considered apart from its role in cooling, then green infrastructure interventions will no longer seem so costly.